1. Field of the Invention
The present invention relates to information handling systems, and more particularly, to the computer memory organization and memory output in graphics display devices.
2. Background Art
Graphics display systems typically receive information for presentation on a video display device in the form of encoded data. The information is stored in a bit plane memory which is organized in a manner that allows it to be scanned by the display controller and converted into control signals to create a final display image. The bit plane memory of a particular display controller is usually organized in a manner that supports the type of video display device for which the controller was designed. For example, the display controller may provide high, medium, or low resolution and support one or more "pages" of data for the display. Accordingly, bit plane data transmitted to the display controller from, for example, an application program, would be stored in the bit plane memory in the format necessary to generate signals for the particular video display.
FIG. 1 depicts a conventional display controller. The application program (running in processor 105) provides a bit plane address 102 indicative of position on the video display for which data is being transmitted. Bit plane data 104 is transmitted from the processor and contains encoded values representing the content of the display. The display controller causes the bit plane data 104 to be stored in bit plane memory 106 at the address specified by bit plane address 102. The display controller causes bit plane memory 106 to be periodically scanned, with the data being converted into serial signals for controlling the video display device by video shift registers 108. Finally, the signals are transmitted to the video display through video connector 110.
A display controller constructed according to conventional techniques is limited to use with the display devices for which it was designed. The introduction of a new, improved video display with, for example, a video connector with different pin assignments, or a different screen display size, is useless with the existing display controller.
A second problem is the need to store data into multiple planes. The display screen is generated as a plurality of scan rows each comprised of a plurality of individual picture elements referred to as pixels or pels. An image is created by having each pel be either on or off. Each pel can therefore be encoded as a single binary unit, or bit, that is either on (1) or off (0). The representation of colors or multiple shades of gray requires an encoding scheme with more than one bit per pel. The use of three bits allows the encoding of 2.sup.3 or 8 colors or shades of gray, for example. Each additional bit creates an additional "plane" of the encoded image. In the example three bit planes are used to store the encoded image.
A character may be generated based on a stored image of the character. The character image, e.g. A, is displayed in a selected foreground color and the background of the character box in a selected background color. In a monochrome, or single bit per pixel memory, the character box and image is simply copied into the bit plane with the image "on" (1) and the background "off" (0).
The use of a display device which allows colors or multiple shades of gray and thus has multiple bit planes, requires a cumbersome analysis to determine the image to be written to each bit plane. In the prior art systems each plane is then written sequentially.
The present invention is directed towards providing a programmable display controller that allows for the creation of multi-format bit planes which in turn may be transmitted to a variety of video displays through a programmable video connector. The present invention is further directed toward providing a display controller that can simultaneously store data in multiple planes of bit plane memory 106.